Magnesium in its ionic form is essential to many physiological processes. It is one of the most abundant cations in the body and, next to potassium, it is the most prevalent intracellular ion. It plays a vital role in carbohydrate and lipid metabolism by serving as an activator of adenosine triphosphate (ATP) in the transfer of energy rich phosphate. It is also essential as an activating ion for many enzymes involved in lipid, carbohydrate and protein metabolism. In muscle tissue, magnesium has a significant influence on neuromuscular apparatus.
The amount of magnesium in the body is particularly significant. Decreased levels of magnesium in the body produce muscle irritability which, if not corrected, can result in involuntary muscle spasms and convulsions. On the other hand, increased levels of magnesium can result in a loss of deep tendon reflexes, a loss of touch, temperature and pain sensation, respiratory failure and cardiac arrest.
Therefore, it has been long recognized that for suitable diagnosis and treatment of various ailments, the accurate and rapid measurement of magnesium ions is important. In addition, it is also important in many environmental monitoring programs and manufacturing processes that magnesium be accurately measured.
Colorimetric methods are known for the determination of the concentration of magnesium ions in various fluids, e.g. groundwater, seawater, wastewater, manufacturing liquids and biological fluids. These methods usually involve adding a reagent to the fluid which forms a colored complex with any magnesium ions present. The complex absorbs electromagnetic radiation at a characteristic wavelength different from that of uncomplexed reagent.
Known methods for determining magnesium have various drawbacks. The fluids to be tested often contain various materials which interfere with the assay. For example, proteins and calcium ions present in fluids can also complex with magnesium complexing dyes, thereby causing an interference.
Hydroxy-substituted cyanoformazan derivatives have been used in the analysis of ions in fluids for some time, as described by Budesinsky et al, Inorg. Chem., 10(2), 313-317 (1971) and Podchainova et al, Zhur. Analiticheskoi Khimii, 32(4), 822-832 (1977). These references describe the complexation properties of several cyanoformazans with various metal ions. One compound specifically described by both references is 1,3-bis(2-hydroxy-5-sulfophenyl)-3-cyanoformazan. While this compound was found to successfully complex with chromium, copper, nickel and a variety of other transition metal ions, it does not selectively complex with magnesium ions at relatively low pH (i.e. less than 10). Other similar cyanoformazans known to complex aluminum ions at pH 4 are described by Malevannyi in Tr. Inst. Khim. Ural. Nauchn. Tsentr, Akad. Nauk SSSR, 30, pp. 55-61 (1974) and Izv. Tomsk. Politekh. Inst., 238, pp. 86-88 (1977). No complexation of magnesium ions is described or suggested in any of these references.
Other cyanoformazan derivatives are described by Feng et al in the Chinese journal Chemical Reagents, 4(4), pp. 219-222 (1982). This reference describes an evaluation of the effect of surfactants on 1,5-bis(2-hydroxy-5-sulfophenyl)-3-cyanoformazan and 1,5-bis(2-hydroxy-5-chlorophenyl)-3-cyanoformazan. However, these compounds must be used at relatively high pH, i.e. greater than 10, for greatest sensitivity for magnesium ions. At a pH below 10, their selectivity for magnesium is low. Further, the 5-sulfophenyl derivative exhibits high background in a magnesium assay. Also, the stability of the dyes decreases with increasing pH, i.e. they tend to break down at higher pH and cannot be stored for an extended period of time.
Hence, there is a need in the art for compounds which have high sensitivity for magnesium ions at relatively low pH.